Oxidation of unsaturated hydrocarbons



United States Patent 3,095,450 OXIDATION OF UNSATURATED HYDRO- CARBONS Adolph C. Shotts, Maplewood, La, assignor, by mesne assignments, to Cities Service Research and Development Company, New York, N.Y., a corporation of New Jersey No Drawing- Filerl Jan. 27, 1960, Ser. No. 4,866 4 Claims. (Cl. 260-597) This invention relates to the preparation of unsaturated carbonyl compounds. More particularly, the invention relates to the oxidation of olefins employing mercury nitrate as oxidizing reagent. Still more particularly, the invention relates to improvements in such a process related to improving and maintaining the activity and effectiveness of the mercuric nitrate.

It has been known heretofore that olefins can be oxidized using mercury salts as the oxidizing agent. It has also been known in the art that the mercury salts, in order to be effective, must be mercuric rather than mercurous in valence state. It is additionally known in the art that the mercuric salts employed for oxidizing the olefins are reduced to the mercurous state by the reaction. Thus, the art has devised several methods for regenerating the mercurous salts back to the mercuric state. All of these methods have involved the use of a strong acid such as sulfuric acid. They additionally have required that the mercurous salt be separated and recovered from the spent or partially spent reagent solution prior to regeneration. Others have employed still more costly and expensive oxidation materials than a strong acid and/or methods such as nitric oxide, chlorine in the presence of acid, electrolytic oxidation, and comparatively high temperatures over extended periods of time.

It is therefore among the objects of this invention to provide a method of oxidizing olefins with mercuric nitrate whereby expensive time-consuming and complicated procedures for reactivating the mercuric nitrate oxidizing reagent are obviated.

It is another and more important object to provide a process of producing unsaturated carbonyl compounds from aliphatic olefins using mercuric nitrate as the oxidizing reagent wherein the activity of the mercuric nitrate is maintained and thereby the mercuric nitrate can be used continuously.

It is yet another object to oxidize cyclic olefins to carbonyl compounds from cyclic olefins.

It is still another object to provide a method of activating spent mercury nitrate reagent without the necessity of separating and recovering it from spent reagent solution.

These and other objects are accompanied by passing an oxygen-containing gas into the mercury nitrate reagent solution. In this simple expedient fashion, the mercury nitrate is easily oxidized to the mercuric state whereby its activity is secured.

By the term olefin as used herein is meant the open chain as well as cyclic olefins. Among the many olefinic compounds which can be oxidized by this process and the oxidizing agent either reactivated or maintained continuously in active form by use of this invention are the illustrative examples: propylene, butene-l, butene-2, isobutylene, pentene l, pentene-2, 3-methyl-butene-1, 2-methylbutene-Z, hexened, hexene-Z, 4-methyl-pentene-1, 3,3- dimethyl-butene-l, 4-methyl-pentene-2, octene-l, butadiene, the pentadienes, the hexadienes, the heptadienes, cyclopentene, cyclohexene, 3-methyl-cyclo-hexene, etc. These compounds and their various homologues and analogues may be substituted in the nucleus and/ or in the substituents in various degrees by straight chain, alicyclic and/ or heterocyclic radicals. The olefins can be treated individually or as mixtures with each other or with the corresponding or other saturated organic compounds. When treated in mixtures, for example, with the corresponding paraffin, the parafiin will remain substantially, if not wholly, unaffected. In other words, by the present process it is possible to selectively oxidize olefins, saturated compounds, if present, acting merely as diluents. Conversions efiectible by the mercuric nitrate and possible with the use of the invention include, for example, the conversion of propylene to acrolein, isobutylene to methacrolein, alphaor beta-butylene to methyl vinyl ketone, pentene-l or pentene-Z to ethyl vinyl ketone and/ or pentene-3-one-2, 2-methyl-butene-2 to methyl isopropenyl ketone, cyclohexene to formyl cyclopentane and the like.

As it can be seen from the case of cyclohexene above, the product resulting from oxidizing cyclic olefins sometimes results in breaking the ring and reforming the ring with a fewer number of carbon-s, the carbonyl group in that case is on the substituent group.

It is to be noted that the vinyl-type carbonylic products obtained while employing the invention are not necessarily those which would be expected from the direct substitution of an oxygen atom for two hydrogen atoms in the allyl position, that is, for two hydrogen atoms attached to a carbon atom separated from the double bond by an intervening carbon atom, for in that case betabutylene, for example, would form crotonaldehyde and not methyl vinyl ketone. Instead, the reaction appears to be initiated at the double bond and proceeds with the elimination of a hydrogen atom from the allyl position and a change in position of the double bond.

Straight chain alpha-olefins of three or more carbon atoms when treated according to the present process tend to yield the same products as the corresponding betaolefins. Thus, as stated above, alpha-butylene as well as beta-butylene yields methyl vinyl ketone and pentene-l like pentene-Z yields ethyl vinyl ketone. This is thought to result from isomerization of these alpha-olefins to the beta-olefins under the reaction conditions.

It is to be understood that the activity of the mercury nitrate catalyst is obtained when oxygen is passed through a reagent solution containing mercury nitrate and an acid such as sulfuric or nitric acid as has been employed by prior art; however, the acids are not necessary in this invention although no deleterious effects result from its presence and thus they can be included.

There are various embodiments in this invention which may be employed. Some embodiments in particular, however, are greatly superior and more desirable; therefore it is pointed out that the second of the following described varying embodiments is not necessarily equivalent. For example, as illustrative but non-limiting examples of the varying embodiments, the invention may be practiced as follows: To a solution of mercuric nit-rate maintained at a suitable reaction temperature, the olefin desired to be oxidized is passed thereinto in a continuous stream. Simultaneously, either in a' separate stream or mixed with the olefin, air or other oxygen-containing gas is passed continually into said mercuric nitrate solution. The olefin charged is converted first to a mercury nitrate-hydrocarbon complex which is subsequently decomposed to form the desired carbonyl compound and mercurous nitrate. The oxygen being charged immediately effects reoxidation of the mercurous nitrate to the mercuric state and thus the oxidative ability of the mercury nitrate is maintained almost indefinitely.

In another embodiment, the olefin is charged for a period of time into the mercury nitrate oxidizing reagent; and when the activity of the mercury nitrate reagent is reduced to a predetermined degree, olefin flow is stopped and oxygen-containing gas is passed into the mercurous nitrate solution until a substantial portion is converted to mercuric nitrate. The flow of oxygen-containing gas is stopped, and olefin again is passed into the oxidizing solution until the activity of the solution is again reduced to a predetermined level. The process of introducing oxygen-containing gas and then olefin is repeated throughout the process.

In still another and the preferred embodiment, the olefin is charged in continuous fashion to a mercury nitrate oxidizing reagent solution and oxygen is also charged either in a separate stream or mixed with the olefin, intermittently, i.e., as ofiten as necessary to maintain the oxidation effected by the mercury nitrate solution at a desired rate. The above embodiment has considerable advantages even over the other embodiments described above.

A wide variation in temperature is satisfactorily employed in the utilization of this invention. This is especially true where the oxidation of the mercury nitrate catalyst is performed in situ during oxidation of the olefin, and in this case the reactivation temperature of the mercury nitrate will be that of the olefin oxidation. In general, the temperatures employed will be between about 20 and about 110 C. I prefer to employ a temperature of about 70 to about 95 C. The preferred temperature in any specific case will vary somewhat depending on the particular olefin to be oxidized. It should be pointed out that it is desirable, particularly where continuous separation is intended, that the temperature should be above the boiling point of the carbonylic product. Thus when it is possible to maintain a reaction temperature above the boiling point of the product, the product is readily and conveniently recovered by merely condensing the vapors as they evolve from the reactor. The elevated temperature also hastens decomposition of the mercuric nitrate-olefin complex which first forms in the reaction. This complex decomposes with evolution with the olefin, and the carbonylic compound and the olefin can be recycled to the oxidizing solution or passed to another oxi- .dation vessel. Of course, the formation and decomposition of the mercury nitrate-olefin complex can be carried out in separate vessels if desired.

The concentration of the aqueous mercuric nitrate which is employed is relatively noncritical, and thus almost any concentration may be employed; however, as a rule, concentrations on the order of about 2% to about 50% will most generally be employed with satisfactory results. If stronger concentrations are employed some difficulty is experienced with foaming.

The term oxygen-containing gas as used hereinabove, includes any mixture of gases containing oxygen, small amounts of ozone in addition, and with any other gases present being inert to reagents or products. Thus air or a stream of molecular oxygen are suitable. I also intend to convey by oxygen containing gas that this is inclusive of a mixture of oxygen and olefin with or without other gases which are inert. These gases are fed to the reactor at about atmospheric pressure, although pressures which are slightly super-atmospheric and subatmospheric pressures may be employed. The oxygen-containing gas is preferably charged at a rate, when charged simultaneously with the olefin, to maintain the activity of the mercury nitrate at all times. In the other embodiments it is charged at a rate to obtain reactivation or substantial reactivation within a time desired.

Example 1 A reagent mixture composed of 43.8 grams of mercuric oxide, 25 ml. of 70.3% nitric acid (specific gravity=1.421) and 400 ml. of water was prepared. The mixture was agitated and heated to 73 C. Isobutylene was passed through a bubble tube into the reagent solution at the rate of 2.44 liters per hour for 5.5 hours. A solid complex formed immediately and began to decompose with evolution of methacrolein and isobutylene. During the reaction time the temperature was gradually elevated to 96 C. to remove all of the methacrolein from the reagent mixture. The product was collected by condensing the vapors into an ice water cooled receiver. Methacrolein in the amount of 1.57 grams (45% of theory, based on mercuric nitrate) resulted.

Example 2 The spent reagent from a reaction similar to that above was agitated and heated to 95 C. while oxygen was passed through the material. When isobutylcne was passed into this regenerated reagent as described above, 2.7 grams of methacrolein resulted.

Example 3 A reagent mixture similar to that of Example 1 Was prepared. The reagent was heated and agitated as in Example 1. Isobutylene at 2.44 liters per hour and oxygen at 2.5 liters per hour were passed through the oxidizing reagent. Methacrolein in the amount of 3.53 grams resulted. This experiment illustrates the catalytic or oxygen carriyng effect of mercuric nitrate.

Example 4 A reagent mixture composed of 65.7 grams of mercuric nitrate, 143 mls. of 70.3% nitric acid and 400 mls. of Water was prepared. The oxidizing solution was heated and agitated as before. Oxygen at 2.5 liters per hour and isobutylene at 2.44 liters per hour were passed into the solution. The temperature was maintained between and C. Methacrolein in the amount of 4.1 grams resulted.

Having thus described the invention by providing specific examples thereof, it is to be understood that no undue limitations or restrictions are to be drawn by reason thereof and that many variations and modifications are within the scope of the invention.

I claim:

1. In a process of oxidizing aliphatic olefins to unsaturated aldehydes and ketones comprising passing an aliphatic olefin of 3 to 8 carbons into an aqueous mercuric nitrate oxidizing solution, the improvement which comprises passing a free oxygen-containing gas into said olefin oxidizing solution.

2. A process according to claim 1 wherein the oxygencontaining gas is introduced continuously into the mercury nitrate oxidizing solution during the olefin oxidation reaction.

3. The process according to claim 1 wherein the olefins are alkenes of 3 to 8 carbons.

4. The process according to claim 1 wherein the temperature of the reaction is about 70 to about C.

References Cited in the file of this patent UNITED STATES PATENTS 

1. IN A PROCESS OF OXIDIZING ALIPHATIC OLEFINS TO UNSATURATED ALDEHYDES AND KETONES COMPRISING PASSING AN ALIPHATIC OLEFIN OF 3 TO 8 CARBONS INTO AN AQUEOUS MERCURIC NITRATE OXIDIZING SOLUTION, THE IMPROVEMENT WHICH COMPRISING PASSING A FREE OXYGEN CONTAINING GAS INTO SAID OLEFIN OXIDIZING SOLUTION. 